Factors influencing the N and P loss from farmland runoff in Dianchi watershed

The present status and influential factors of N and P loss from farmland runoff were studied in 15 villages and towns around Dianchi Lake.The results show that the pollutional loads of N and P in farmland runoff in the investigated areas are very high.The mean annual discharges of N and P are different greatly,the total N is 5.07～113.16kg/hm² and the total P is 0.15～10.14kg/hm².Excessive application of fertilizer is the primary reason of large N and P loss,which is also related to the land use pattern,water and soil management,and farming system.The discharges of N and P vary with slopness,increase rapidly with the slopness from 6° to 12°and increase slowly with the slopness above 12°.In a rainfall or in a crop growing period,the concentrations of N and P in the runoff submit to a downtrend following the temporal process.The discharges of N and P vary with different fertilizer applications and urea and superphosphate application can reduce the N and P loss and heighten the cabbage yield.